In the simplest construction, PSA transfer tapes comprise an unsupported PSA film coated onto a release liner. Transfer tapes are commonly used in a variety of mounting applications, for example, mounting name plates, signs, posters, pictures, bulletin boards, and the like to walls. In these applications, the PSA film is required to provide sufficient shear adhesion to prevent the two bonded substrates from creeping away or separating from each other. For example, when a poster is adhered to a wall, it is desirable that the PSA film provide sufficient shear strength so that the poster does not move or fall off the wall due to the weight of the poster.
At the same time, it is often desirable to be able to detach the bonded substrates from each other without damage to one of the substrates, for example, when one substrate is more valuable or more easily damaged than the other. To facilitate detachment without substrate damage, the opposite major surfaces of the PSA film preferably provide different levels of peel adhesion that are suitable for the particular substrate to which they are attached. For example, the major surface of the PSA film in contact with a poster preferably provides lower peel adhesion than the major surface in contact with a wall to facilitate removal without damaging the poster. Alternatively, when damage to the wall is to be avoided, the major surface of the PSA film in contact with the wall preferably provides lower peel adhesion than the major surface in contact with the poster.
One way to provide different peel adhesion properties is to provide a double-sided tape comprising a core or inner layer having a different adhesive layer on each side. An example of one such double-sided tape is commercially available from 3M as Scotch.TM. High Tack/Low Tack Double Coated Tape.
While such tapes have proven useful, a need exists for a PSA film having good shear strength and opposite major surfaces which provide different levels of peel adhesion without the need for a core layer and preferably without the need for separate adhesive coatings. Such a construction is simpler than tapes requiring a core layer and separate adhesive coatings, and is therefore easier to produce. In addition, the peel adhesion differential provides removability without substrate damage.